1. Field of the Invention
The invention relates to a real image direct front projector including a housing with a plane transparent object support on which the object is placed and which permits light emanating from at least one light source to pass through, with a projection lens for converging the reflection rays emanating from the object for producing an object image on an image wall outside of the projector, and possibly with an auxiliary mirror.
2. Description of the Related Art
Direct front projectors of this type, also called episcopes, serve for producing a real image of an object, for example, a document, a photograph or the like, with the use of light rays which emanate from a light source, are conducted over a reflector mirror, are reflected irregularly by the object and are cast onto an image wall and a projection lens.
In the real image projectors which are usually used, in which an object is placed on an object support composed of glass or a similar material and is subjected to direct light rays from at least one light source, auxiliary mirrors for reflecting the light reflected by the object and the projection lens are arranged in a housing. In that case, the light source must be arranged in such a position that it is ensured that, in order to avoid an impairment of the dissolution of image formed as a result of the regularly reflected light, the light rays emanating from the light source and reflected by the object support in accordance with the object and regularly reflected by the object support in accordance with the reflection laws are not cast over the auxiliary mirror to the projection lens. Moreover, the light source must be arranged outside of the angular coverage of the projection lens and the light source must be arranged far away from the object table in order to uniformly illuminate the object table.
In order to avoid these disadvantages, real image direct front projectors are known in which auxiliary mirrors are mounted parallel to the optical axis and laterally next to the projection lens. These auxiliary mirrors have the purpose of permitting the light emanating from the light source arranged next to the projection lens to be cast obliquely onto the object support, in order to prevent these rays from reaching the projection lens by being reflected at the object support as a result of the law of reflection and from being cast as disturbing bright spots onto the image wall and impairing the image quality. In such an embodiment of a real image direct front projector, the object support is illuminated very irregularly because the laterally mounted light source--several light sources are also possible--is arranged asymmetrically relative to the object support. In addition, the light radiating obliquely onto the object support results in a significantly reduced and defused light reflection from the object to the projection lens than would be the case if the light rays are directed almost perpendicularly onto the object and are deflected with a greater reflection light to the projection lens.
Therefore, the invention is based on the object of providing a real image direct front projector which has a small dimensions and ensures a uniform, optimum illumination of the object and prevents harmful reflected light.
For meeting this object, the invention proposes in a real image direct front projector of the above-described type to provide the object support on its side facing away from the object and over a predetermined area with a plurality of microprisms.
As a result of this configuration, the light source, or a plurality of light sources, can be arranged in the vicinity of the projection lens, so that a substantially uniform optimum illumination of the object support and, thus, of the object is ensured. The reflected stray light rays are deflected next to the entry area of the projection lens, so that harmful reflected light on the image wall is prevented. This is also achieved when an auxiliary mirror is arranged between the object support and the projection lens.
Additional features of a real image direct front projector according to the invention are disclosed in claims 2 to 8.